###
Arguments

####
N

An integer specifying the order of E_{
n}
(*
x*
). *
N*
can be either a scalar or an array.

####
X

The value at which E_{
n}
(*
x*
) is evaluated. *
X*
can be either a scalar or an array.

Note: If an array is specified for both *
N*
and *
X*
, then EXPINT evaluates E_{
n}
(*
x*
) for each *
N*
_{
i}
and *
X*
_{
i}
. If either *
N*
or *
X*
is a scalar and the other an array, the scalar is paired with each array element in turn.

###
Keywords

####
DOUBLE

Set this keyword to force the computation to be done in double-precision arithmetic.

####
ITMAX

An input integer specifying the maximum allowed number of iterations. The default value is 100.

####
EPS

Use this keyword to specify a number close to the desired relative error. For single-precision calculations, the default value is 1.0 *
¥*
10^{
-7}
. For double-precision calculations, the default value is 1.0 *
¥*
10^{
-14}
.

###
Example

To compute the value of the exponential integral at the following X values:

X = [1.00, 1.05, 1.27, 1.34, 1.38, 1.50]

result = EXPINT(1, X)

PRINT, result

IDL prints:

0.219384 0.201873 0.141911 0.127354 0.119803 0.100020

This is the exact solution vector to six-decimal accuracy.